The invention pertains to methods of vaporizing materials, and to methods of cleaning vaporization surfaces. In further aspects, the invention encompasses vapor forming devices comprising plasma generation circuitry configured to utilize a vaporization surface as a plasma electrode.
Vapor forming apparatuses have many applications in modern semiconductor processing. Among the applications is utilization in chemical vapor deposition apparatuses. An exemplary chemical vapor deposition apparatus 10 is described with reference to FIG. 1. Apparatus 10 comprises a reaction chamber 12 having a substrate holder 14 contained therein. A substrate 16 is shown supported by substrate holder 14. Substrate 16 can comprise, for example, a semiconductive material wafer, such as, for example, a wafer of monocrystalline silicon.
Chamber 12 has a vapor inlet 18 extending therethrough and a vapor outlet 19 also extending therethrough. Accordingly, a vapor (illustrated by arrows 20) can be flowed through chamber 12.
Chamber 12 can comprise one or more temperature control mechanisms (not shown) which can include, for example, heaters, or cooling gas flow ports. The thermal controls can enable substrate 16 to be maintained in a temperature such that a material is deposited onto substrate 16 from the vapor 20 within chamber 12.
A vapor forming device 30 is provided to generate vapor 20. Device 30 comprises an inlet region 32 configured to enable flow of a non-vapor state material 33 into device 30. Device 30 further comprises an inlet port 34 configured to enable flow of a carrier gas 35 into device 30. Additionally, device 30 comprises an outlet port 36 configured to enable vapor-state-material 20 to be output from device 30 and into reaction chamber 12 of apparatus 10.
A vaporizer 40 is within device 30 and supported by a holder 42. Vaporizer 40 comprises a surface 44 which can be referred to as a vaporization surface. Vaporizer 40 can comprise a heated material such that non-vapor-state-material 33 is converted from a non-vapor-state to a vapor-state upon contacting vaporization surface 44.
Material 33 is typically initially in the form of a liquid, and is flowed into device 30 from a holding reservoir 46. Although in the shown exemplary embodiment only one non-vapor-state material 33 is flowed into device 30, it is to be understood that a plurality of different non-vapor-state materials can be flowed simultaneously into device 30 to form a vapor 20 comprising a composite of vapors from the various materials. An exemplary application in which a plurality of non-vapor-state materials are flowed into device 30 is a chemical vapor deposition process for formation of barium strontium titanate (BST).
Two separate configurations of prior art vaporizer devices 30 are described with reference to FIGS. 2 and 3.
Referring first to FIG. 2, a first prior art vaporization device 30 is illustrated in diagrammatic, schematic view. Such device comprises a COVA device (COVA Technologies, Inc., 2260 Executive Circle, Colorado Springs, Colo. 80906).
The vaporization device 30FIG. 2 comprises vaporizer 40 which includes a pillar 60 extending upwardly into the device. Holder 42, to the extent there is one in the device of FIG. 2, is defined by a bottom portion of pillar 60. The device 30 of FIG. 2 further includes a thermally conductive material 50 defining a void 52 therein. Material 50 is shaped to define an outer periphery 54 comprising sides 56 and ends 58. Material 50 is further configured to form pillar 60, which protrudes upwardly from one of the ends 58 and into a region between sides 56. The outlet region 36 and inlet region 34 of the device of FIG. 2 extend through material 50 to define gas passageways into and out of void region 52.
Non-vapor-state-material inlet 32 comprises three separate capillaries (32a, 32b, and 32c) extending through an end 58 and terminating above pillar region 60. Non-vapor-state material 33 comprises three separate materials (33a, 33b and 33c), which can comprise, for example, liquids.
In operation, material 50 is heated and non-vapor state materials 33a, 33b and 33c are flowed through inlets 32a, 32b and 32c and onto pillar region 60. The non-vapor state materials are then vaporized upon contact with a heated vaporization surface of pillar region 60 to form a vapor 20. Such vapor 20 then flows to outlet 36 and out of device 30. The three materials 33a, 33b and 33c can comprise, for example, Ba(THD)2, Sr(THD)2, and Ti(Oxe2x80x94iPr)2(THD)2, in, for example, applications wherein a vapor is to be formed for deposition of BST. In the above formulas, THD stands for bis(2,2,6,6-tetramethyl-3,5-heptanedionate) (C11H19O2), and Oxe2x80x94iPr stands for isopropoxide (C3H7O).
In the above-described application for forming BST, material 50 and pillar region 60 are preferably heated to a temperature of about 250xc2x0 C. (Ba(THD)2 vaporizes at about 212xc2x0 C.). Also, the carrier gas 35 preferably comprises a temperature of about 250xc2x0 C. Carrier gas 35 can comprise, for example, nitrogen or helium.
A second prior art vaporization device 30 is described with reference to FIG. 3. In the device of FIG. 3, vaporizer 40 comprises a heated frit, and holder 42 comprises a pair of projections extending from sides of frit 40. The embodiment of FIG. 3 further comprises an outer periphery 70 surrounding frit 40 and defining a void 72 therein. Inlet region 32 comprises three separate capillaries (labeled as 32a, 32b and 32c) which extend through periphery 70 and into void regions 72. Capillaries 32a, 32b and 32c are configured such that non-vapor-state-materials 33a, 33b and 33c flow through capillaries 32a, 32b and 32c and onto a vaporization surface 44 of frit 40.
In operation, frit 40 is heated to a temperature such that materials 33a, 33b and 33c are vaporized upon contact with surface 44 to form a vapor 20 which exits device 30 through outlet port 36. Also, a carrier gas 35 is injected into device 30 through inlet port 34 to flow vapor 20 out of device 30. Materials 33a, 33b and 33c can comprise, for example, Ba(THD)2, Sr(THD)2, and Ti(Oxe2x80x94iPr)2(THD)2, for formation of BST. In such embodiments, frit 40 is preferably heated to a temperature of about 250xc2x0 C., and carrier gas 35 is also preferably heated to a temperature of about 250xc2x0 C. The system described with reference to FIG. 3 is a diagrammatic, schematic view of an Advanced Delivery and Chemical Systems vaporizer. (Advanced Delivery and Chemical Systems (ADCS), 7 Commerce Drive, Danbury Conn. 06810-4169.)
A problem with the prior art devices described above is that materials injected into the devices can decompose to form deposits on vaporization surfaces 44. A reason that the deposits form can be, for example, that the vaporization temperature is close to a decomposition temperature for non-vapor-state-materials 33 injected into devices 30. The deposits can decrease the effectiveness of vaporization surfaces 44, and can, for example, cause clogging and other problems due to particulate formation. Accordingly, it would be desirable to develop methods for cleaning deposits from surfaces 44.
In one aspect, the invention encompasses a method of utilizing a vaporization surface as an electrode to form a plasma within a vapor forming device.
In another aspect, the invention encompasses a method of chemical vapor deposition. A vaporization surface is provided and heated. At least one material is flowed past the heated surface to vaporize the material. A deposit forms on the vaporization surface during the vaporization. The vaporization surface is then utilized as an electrode to form a plasma, and at least a portion of the deposit is removed with the plasma.
In another aspect, the invention encompasses a vapor forming device. Such device includes a non-vapor-state-material input region, a vaporization surface, and a flow path between the non-vapor-state-material input region and the vaporization surface. The device further includes a vapor-state-material output region, and a vapor flow path from the vaporization surface to the vapor-state-material output region. Additionally, the device includes a first plasma electrode spaced from the vaporization surface, and plasma generation circuitry configured to utilize the vaporization surface as a second plasma electrode such that a plasma can be formed between the first and second plasma electrodes.